1. Field of the Invention
The present invention relates to a mobile communication system, particularly relates to a mobile communication system and a method for restricting incoming calls when a particular mobile communication exchange is under traffic congestion state.
2. Description of the Related Art
A block diagram of constitution of a general mobile communication system focusing to a network side is shown in FIG. 3.
A location register 31, which manages location information and subscriber information of each mobile station 34, is respectively connected to mobile communication exchanges 32 and 33 for call connecting processing via a common channel signaling network 35 and information required for the processing of an incoming call to each mobile station 34 is mutually communicated via the common channel signaling network 35. Although radio base stations and radio base station control units are not shown in drawings, it is assumed that they are part of the mobile communication exchange 32, 33.
In this type of mobile communication system, if the traffic of a specific mobile communication exchange has increased and congestion state occurs, the specific mobile communication exchange is relieved from such a congestion state by restricting an incoming call to the above mobile communication exchange from other mobile communication exchanges and restricting or denying a call origination request from mobile stations under control of the mobile communication exchange through radio base stations (not shown).
FIG. 4 is a sequence diagram showing a conventional type incoming call control method.
Suppose that the mobile communication exchange 33 which controls the mobile station 34 is in a state of congestion.
At this time, when one of the mobile communication exchanges of the mobile communication network, e.g. the mobile communication exchange 32, receives a request 40 for call termination to the mobile station 34, which is under control of the mobile communication exchange 33, the mobile communication exchange 32 sends an incoming call information reading request 41 to the location register 31 through the common channel signaling network 35.
The mobile communication exchange 32 acquires the location information of the mobile station 34 based upon an incoming call information reading response 42 returned from the location register 31 in response to the above request.
The mobile communication exchange 32 recognizes that the mobile station 34 is located in area under control of the mobile communication exchange 33, and sends a request for call termination 43 to the mobile communication exchange 33.
On the other hand, the mobile communication exchange 33 receives the request 43 for call termination to the mobile station 34, however, as the mobile communication exchange 33 itself is in a state of congestion, the mobile communication exchange 33 returns an incoming call denying signal 44 to the mobile communication exchange 32. Hereby, processing for the call in the mobile communication exchange 32 is interrupted, and the call is treated as a call loss.
However, in such a conventional type mobile communication system, as processing for an incoming call to a mobile station located in an area under control of a mobile communication exchange, which is in a state of congestion, is advanced up to the mobile communication exchange, and the incoming call request is denied by the mobile communication exchange. That is, the mobile communication exchange in a state of congestion is required to execute processing for denying the incoming call. Therefore, such processing for rejecting the incoming call by the mobile communication exchange in a state of congestion causes a problem that a mobile communication exchange in a state of congestion is prevented from recovering from the congestion.
To solve the above problem, Japanese Patent Publication Laid-open No. Hei 3-42950 discloses a technology that incoming calls to an exchange in a state of congestion are rejected at an exchange of the preceding stage which is notified by the exchange in a state of congestion that the exchange is currently being in a state of congestion. Hereby, as incoming calls to an exchange in a state of congestion are restricted at the preceding exchange, the above problem can be solved, however, there is a problem that wasteful processing for incoming calls routed up to the preceding exchange cannot be reduced.